Taking Advantage of a Destructive Insect’s Weakness for Purple

WEST POINT, N.Y. — The cartoon-purple boxes are hard to miss. The foresters who hang them from roadside trees all over the country call them Barney traps, for the friendly dinosaur whose color they resemble, but their purpose is anything but gentle.

The three-sided contraptions, baited with a chemical lure and coated with glue, are designed to catch the attention of the emerald ash borer — a deceptively pretty little beetle from Asia that has killed tens of millions of ash trees in less than a decade.

“Right now, the emerald ash borer is the most destructive insect we have in North America,” said Nathan Siegert, an entomologist with the United States Forest Service.

Named for its wing covers, which look so much like emeralds that people in some countries string them into jewelry, the borer is thought to have come to North America in wooden pallets from China. Since they were discovered near Detroit in 2002, the beetles have spread to 15 states and Ontario.

It also makes great firewood, and foresters say the beetles’ rapid advancement has been aided by campers who unknowingly carry the infested wood, moving the beetles farther and faster than they could fly on their own.

Except for woodpeckers and a few parasitic wasps, nothing stops these shiny little bugs from depositing their eggs in the diamond-shaped bark of all varieties of ash. The larvae then burrow under the bark and feast on the living tissue of the trees for a year or two, eventually cutting off their water supply and killing them. Adult beetles bore their way out of the tree, leaving a telltale D-shaped hole.

Though no one is raising a surrender flag, the ash borer has already spread so far that eradication is no longer considered a possibility. Instead, officials want to slow the spread, aiming to protect as many of the nation’s 9.5 billion ash trees as possible. The Barney trap is the strategy’s centerpiece.

The Forest Service, which developed the trap, distributed 61,500 of them this summer to state and local conservation groups in 48 states, including those where ash borers had not yet been detected.

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PRETTY LITTLE KILLER Barney traps — named for their purple color, like the television dinosaur — detect infestations by the emerald ash borer.Credit
APHIS

The traps are not meant to catch enough beetles to reduce their number. Rather, they are designed to detect the leading edge of an ash borer infestation. If officials know where the beetles are, and where they are going, they have a chance to slow them down.

Finding even one beetle in a trap will set off federal and state quarantines, as happened this summer when an emerald ash borer was found at the United States Military Academy here, 60 miles north of New York City. Knowing that West Point’s 16,000 acres were in the path of the ash borer onslaught, Robert G. MacKenzie, a forester who works for the military academy, had volunteered in May to put up Barney traps.

He hung 16 traps in healthy ash trees at the center of the academy’s grounds. Each side of the trap is corrugated plastic, 14 inches wide by 24 inches high and tinted a deep purple; inside is a chemical lure known to attract emerald ash borers. The panels are folded to form a prism and covered in a glue that ensnares the insects.

On July 13, Mr. MacKenzie lowered one trap and found a single insect that looked like an ash borer. Once the Forest Service confirmed the find, all of Orange County, N.Y., was put under federal quarantine, which prevents the interstate transportation of any ash wood or ash wood products. A state quarantine, which restricts some movement within New York, was added in August.

Only two other beetles were found at West Point, suggesting that it was early enough to try a preventive strategy. One option is to inject trees with insecticide, but that can cost several hundred dollars per tree, and is not practical for large stands.

Instead, West Point conservators have decided to cut down about 78 ash trees that are so close to buildings that they would cause serious damage if they become infested and fall. The countless ash trees in West Point’s woods will be monitored, but not cut down.

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Although foresters for years have relied on detection traps to survey the movement of other destructive insects, like gypsy moths, they have not been used until now to attract these buprestids, or jewel beetles, because they do not respond as readily to chemical lures. To detect the emerald ash borer, entomologists at the United States Department of Agriculture’s Animal and Plant Health Inspection Service first had to do some detective work, getting behind the beetles’ eyes and antennas to find out what turns them on.

The first clue, said Victor Mastro, director of that service’s pest control laboratory in Otis, Mass., came from simply getting a good look at the insect. It is smaller than a penny, with a coppery red belly and huge eyes. Mr. Mastro said that if a human being had eyes that were proportionally as large as the ash borer’s, they would be the size of softballs.

“We suspected that because of their eye size and their coloration, they were visual insects,” Mr. Mastro said.

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The emerald ash borer.Credit
Jim Zablotny

He and his team experimented with a dozen different colors to see which ones attracted the most beetles. They tried greens, reds and some light shades of purple. To round out the dozen they threw in deep purple. “We figured it was probably not a good color, but we put it in as a negative control,” Mr. Mastro said.

The deep purple, it turned out, was the beetles’ antennas-down favorite. Mr. Mastro theorizes that the bugs link the color to the purplish hue that can be seen on the inner bark of ash trees. But no one knows for sure.

With the color decided, the team had to settle on the right shape. Four-sided traps gave them the most surface area, but manufacturing three-sided prisms was far cheaper. Each one costs about $9.

To enhance the traps’ ability to attract beetles, Mr. Mastro said a chemical lure was added. The most effective proved to be manuka oil, an extract from a tree that has been used by Maori tribesmen in New Zealand to treat certain illnesses. (Manuka is widely used in the West for aroma therapy.) Each lure packet contains a blend of manuka and other scents and costs $5.

With New York State in the ash borers’ cross hairs this summer, the state is spending $1 million to survey and stop the spread of the beetles, which have been found in 19 counties. Foresters have placed 6,560 Barney traps across the state, hanging them in state lands and, in some instances when the owners agreed, on private property. Extra traps are hung in target areas, like campgrounds, where the insects are more likely to be found.

At first, state foresters were not enthusiastic about joining the fight. “My initial thought was: ‘It’s over. Move on. Focus on something else where the things we do can make a difference,’ ” said Michael J. Callan, a forester with the New York State Department of Environmental Conservation office in New Paltz.

But Mr. Callan said he soon realized that fighting back made sense. With advance information from the Barney traps, state foresters have been able to set up what they call “sink trees.” A strip of bark about six inches wide is removed all the away around the trunk of each tree, so that great numbers of beetles are drawn to one location instead of spreading throughout a forest. In winter, the sink trees will be cut down, and most of the larvae will die.

Joe Martens, the conservation department’s commissioner, said New York was now on the front line of the battle against the emerald ash borer. The state was trying to hold the line at the Hudson River, because “if it hops across the Hudson, all of New England is next,” he said.

Mr. Martens said the Barney traps had helped raise public awareness of the onslaught and bought time for scientists to learn more about the ash borer, for natural predators like woodpeckers to develop a greater taste for the beetles, and for communities to take steps to mitigate the impact of infestations.

“The stakes are really high,” he said. “But if we don’t arrest the spread of these pests, we have no chance of winning the battle.”

A version of this article appears in print on September 13, 2011, on Page D3 of the New York edition with the headline: Taking Advantage of a Destructive Insect’s Weakness for Purple. Order Reprints|Today's Paper|Subscribe